Electron-discharge device of the magnetron type



J. L. BARTTRO Aug. 28, 1951 ELECTRON-DISCHARGE DEVICE OF THE MAGNETRON TYPE Filed Sept. 24, 1946 2 Sheets-Sheet 1 Twmlm Aug. 28, 1951 J. L. BARTTRO Filed Sept. 24, 1946 2 Sheets-Sheet 2 //1/ V5 /V T01? ATTX Patented Aug. 28, 1951 ELECTRON-DISCHARGE DEVICE OF THE MAGNETRON TYPE James L. Earttro, Watertown, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application September 24, 1946, Serial N 0. 699,007

4 Claims.

This invention relates to electron-discharge devices, and more particularly to electron-discharge devices of the so-called magnetron type.

An object of this invention is to reduce the loss of energy by heat in devices of the above type.

Another object is to allow less intense magnet 10 fields to be used, in a magnetron, for the same output power.

A further object is to increase the efficiency of magnetrons.

A still further object is to more effectively utilize the electrons emitted from the cathode of a magnetron.

Another object is to devise a novel cathode for magnetrons.

The foregoing and other objects of the invention will be best understood from the following description of an exemplification thereof, reference being had to the accompanying drawings, wherein:

Fig. 1 is a fragmentary longitudinal sectional view taken substantially through the center of an electron-discharge device made in accordance with the principles of the present invention; and

Fig. 2 is a transverse sectional view taken along line 22 of Fig. 1.

Referring, now, to the drawings, the numeral 1 generally designates an electron-discharge device of the magnetron type.

As herein shown, said device includes an anode 2, a cathode structure 3, and magnetic means 4 for establishing a magnetic field in a direction transversely of the electron path between said cathode structure and said anode.

The cathode structure 3 preferably comprises a cylindrical body or envelope 5, made of highly conductive material, such as copper, and provided with a plurality, here shown as eight, of cathode members in the form of interiorly-extending, radially-disposed vanes 6.

The cylindrical body 5 is closed at its ends by plates 1 and 8, the junctions between said body and said plates being hermetically sealed, as at 9.

The cylindrical body 5 is of such diameter, and the number, size and relative spacing of the vanes 6 are so chosen that each pair of adjacent vanes, together with that portion of said cylindrical body lying therebetween, defines a cavity resonator at the frequency desired of the output of the device.

The anode 2, which is coaxial with the cathode structure 3, preferably comprises a wire ill, for example of copper or tungsten, of relatively small diameter, this wire extending throughout the length of body 5.

In order to support the anode wire Ill with respect to the cathode members 6, said Wire is rigidly attached at its lower end to the inner conductor I! of a coaxial or concentric cable ii, the outer conductor I3 of which is threadedly secured and hermetically sealed to a pole piece [5. The space between inner conductor II and outer conductor 13 of cable I2 is hermetically sealed, as by insulating means [4. A tubular pole piece It is hermetically sealed, as at it, into the end plate 8, said pole piece being provided with a bore I? through which the cable 12 may enter the device.

In order to extract power from the device, I may, for example, hermetically seal the upper end of anode wire [6, as by a glass bead .43, into a threaded nipple 44 which is in turn threaded and hermetically sealed to end plate 1, said upper end of anode wire 15 being adapted to be connected, by means of a detachable coupling [8, to the inner conductor [9 of a second coaxial or concentric cable 26 similar to cable l2, the outer conductor 2| of cable being connected, as by means of the threaded coupling shown, to the upper end of nipple 44.

Another pole piece 22 is hermetically sealed, as at 23, into the end plate 1, said pole piece, and the pole piece [5, being fixed, for example, at the opposite ends of a horseshoe magnet (not shown), the two pole pieces and the horseshoe magnet constituting the above referred to magnetic means 4 for establishing a magnetic field transversely of the electron path between the anode and cathode structures of the device.

It will be noted that the vanes S are of substantial thickness, and that each vane has a vertical surface which extends parallel to wire anode ill. The said vertical surface of each vane, which is the part of each vane adjacent to Wire anode Ill, is provided with a highly electron-emissive coating 24, for example, of the well-known aka-- line-earth metal oxide type.

Each of the vanes 5 is provided, contiguous to the vertical coated surface thereof, with a ver-, tically-e'xtending aperture 25, in which is positioned a heating filament 26, each of said filaments being connected at one end 21 to its cor responding vane 6, and at its other end 28 to a common lead-in conductor 29, of circular configuration, which is positioned below the lower edges of vanes 6. Conductor 29 is led electrically to the exterior of the device I by means of a main conductor 30 which enters said device through a pipe 3| threaded and hermetically sealed into the cylindrical side wall of envelope 5. Current may be conveyed to filaments 26 by connecting an appropriate source of direct current 32 between conductor 38 and envelope 5, lead 33 extending between one side of source 32 and conductor 3i], and lead 34 extending between the other side of said source and envelope 5.

In order to increase the effectiveness of the cavity resonators defined by the cathode structure 3, I provide the vanes 6, preferably, in both the upper and lower edges thereof, adjacent their inner ends, with slots 35 receptive of two pairs of concentric conductors or straps 36 and 31, and 38 and 39, the straps of each pair thereof alternately contacting successive vanes 6.

The cathode and anode structures of the device may be maintained at a proper potential difference, for example, by connecting the inner conductor ll of cable i2, through a conductor 40, to the positive terminal or" a source dl of direct current, and by connecting the cathode structure 3, through a conductor is, to the negative (grounded) terminal of said direct current source.

In the magnetron, it is not desired to attract to the anode from the cathode the largest possible number of electrons in the shortest possible transit time, but rather to create a definite path of sufficient length to enable one, by the use of resonant cavities, to extract the maximum amount of wave motion from the spiraling electrons; therefore, it is desired to increase the electron transit time, so that more energy can be absorbed from each electron.

In the magnetrons of the conventional type, in which an anode of relatively large diameter surrounds the cathode or electron emitter, large numbers of electrons find their way, in a relatively short time, to the anode, striking it at high speeds, resulting in the wasteful production of heat, or in the liberation of gas, or in the dislodging of electrons from the anode which wastes energy b secondary emission and consequent dynatron action.

However, in the magnetron oi this invention, the anode ii is relatively small, and it is surrounded by the e'lectron-emitting surfaces of the vanes, which are all at a negative potential with respect to said anode. Electrons are emitted from the coatings 2 3 on the interior vertical surfaces of the vane 8 in random directions and proceed toward the anode iii, being defiected clockwise or counterclockwise (depending on the polarities of pole pieces iii and 22) by the magnetic field of magnetic means 4. Due to the small size of the wire anode iii, large numbers of the electrons miss the anode and proceed beyond it toward a vane 6 beyond the anode. A few of the electrons strike the anode and give up their energy as heat. In general, however, electrons pass by the anode with the velocity acquired in the cathode-anode transit. In the region on the opposite side of the anode wire, the electric field is in the opposite direction, due to the negative potential of the cathode vanes; therefore the electrons are slowed down in this region, come to rest, and are repelled or moved back toward the anode [0. This is similar to the action of the retarding-field oscillator.

A substantial number of electrons again miss the anode wire, are again repelled on the opposite side, and after a plurality of such passages back and forth finally come to rest on the anode with a relatively low velocity. As a result, large numbers of the emitted electrons miss the anode for relatively long periods of time, thereby oscillating back and forth over a relatively long transit time i of the envelope 5.

d and giving up more energy to the resonant cavities, so that a stronger wave motion per electron emitted is set up in the resonant cavities.

The frequency of the oscillations set up is dependent only on the geometry of the device I and on the applied voltage; of course, as the electrons travel back and forth between opposite sides of the anode wire in the above-described manner, they also move clockwise or counterclockwise due to the action of magnetic means 4, so that they follow a spiral path and set up oscillations in the resonant cavities.

Since the electrons strike the anode, finally, with relatively low velocities, the heat developed by such collisions is a minimum, so that the heat losses are reduced and the efficiency of the magnetron correspondingly increased. Because the transit time of the electrons is made rather large by this invention, the electrons emitted from the cathode are more effectively utilized, since more energy is abstracted from each electron.

In the prior art magnetrons, it was necessary to increase the strength of the transverse magnetic field in order to achieve longer platecathode electron transit times, to thereby utilize the electrons more efiectively. This is true because, with a strong enough magnetic field, the electrons may not reach the anode, but instead may return to the cathode. However, with this invention, due to the longer transit time inherent in the construction of the device, it is possible to lower substantially the magnetic field strength required for the same output power; in fact, the said magnetic field strength may be lowered to a value which is one-fifth to one-third of that formerly required for the same output power. The monetary savings resulting from this reduction are obvious.

Due to the relatively large electron-emitting area, which is the combined area of the interior vertical surfaces of all of the vanes, 6 it is possible to produce copious quantities of electrons, substantially more than the number produced in the prior art devices, to thereby obtain a greater power output from the device.

Of course, it is to be understood that this invention is not limited to the particular details as described above, as many equivalents will suggest themselves to those skilled in the art. For example, instead of the cathode heating means shown, it is possible to use other heating means, such as an external radio-frequency field applied to device by winding a radio-frequency output coil around the exterior Various other variations will suggest themselves. It is accordingly desired that the appended claims be given a broad interpretation commensurate with the scope of this invention within the art.

What is claimed is:

1. An electron-discharge device comprising: an anode; a thermionic emission cathode structure, surrounding but spaced from said anode, and including a plurality of radially-disposed cathode members; each pair of adjacent cathode members, together with that portion of said cathode structure lying therebetween, defining a cavity resonator; and means, supported adjacent said anode and said cathode structure, for establishing a substantially uniform magnetic field in a direction transversely of the electron path between said cathode structure and said anode.

2. An electron-discharge device comprising: an anode; a thermionic emission cathode structure, surrounding but spaced from said anode and including a plurality of radially-disposed vanes; each pair of adjacent vanes, together with that portion of said cathode structure lying therebetween, defining a cavity resonator; an electron-emissive coating on the part of each of said vanes adjacent said anode; and means, supported adjacent said anode and said cathode structure, for establishing a substantially uniform magnetic field in a direction transversely of the electron path between said parts of the vanes and said anode.

3. An electron-discharge device comprising: an anode wire of small diameter with respect to the, diameter of said device; a thermionic cathode structure, surrounding but spaced from said anode, and including a metallic envelope having a plurality of radially-disposed vanes mounted therein; said vanes each having a surface extending parallel to said anode wire; each pair of adjacent vanes, together with that portion of said envelope lying therebetween, defining a cavity resonator; an electron-emissive coating on said surface of each of said vanes; means for heating each of said coatings to the temperature of thermionic emission; and means, supported adjacent said anode and said cathode structure, for establishing a substantially uniform magnetic field in a direction transversely of the electron path between said vane surfaces and said anode.

4. An electron-discharge device comprising: an anode wire of small diameter with respect to the diameter of said device; a thermionic cathode structure, surrounding but spaced from said anode, and including a metallic envelope having a plurality of radially-disposed vanes mounted therein; said vanes each having a surface ex= tending parallel to said anode wire; each pair of adjacent vanes, together with that portion of said envelope lying therebetween, defining a cavity resonator; an electron-eniissive coating on said surface of each of said vanes; a plurality of heaters, one being positioned closely ad jacent said surface of each of said vanes; said heaters being adapted to heat each of said coatings to the temperature of thermionic emission; and means, supported adjacent said anode and said cathode structure, for establishing a sub stantially uniform magnetic field in a direction transversely of the electron path between said vane surfaces and said anode.

JAMES L. BARTTRO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,108,900 Peterson Feb. 22, 1938 2,114,114 Roberts Apr. 12, 1938 2,121,067 Brown et a1 June 21, 1938 2,163,157 Samuel June 20, 1939 2,180,279 Farnsworth Nov. 14, 1939 2,184,910 Farnsworth Dec. 26, 1939 2 ,190,668 Llewellyn Feb. 20, 1940 2,227,909 Ohl Jan. 7, 1941 2,443,445 Donal, Jr. et a1. June 15,, 1948 2,482,495 Laidig Sept. 20, 1949 

